Gameplay revolves around the "Aperture Science Handheld Portal Device" (ASHPD), a handheld device that can create portals on flat planes, allowing instant travel and a visual and physical connection between any two different locations in 3D space. Portals are restricted to planar surfaces, but if two linked portals are on different planes, bizarre twists in geometry and gravity can occur, such as the player walking through a portal on the wall and "falling" up out of the floor several feet behind where he started. Only two portals may be open at a time. If a new portal is created, it replaces the previous portal of the same color. The device also acts as a less powerful version of Half-Life 2's gravity gun, which can grab and hold objects, though it is not able to 'punt' objects as the Gravity Gun can.